1. Technical Field
The present invention relates to an autowiper controller for a vehicle which automatically actuates a wiper in the rain.
2. Description of the Related Art
There is an autowiper controller for automatically actuating a wiper when it rains during a running operation of a vehicle.
In order to detect a rainfall, a raindrop detecting surface is set to a windshield to utilize a change in a reflectance of a light when a waterdrop adheres to the raindrop detecting surface.
In other words, an infrared light is irradiated from a light emitting device onto the raindrop detecting surface, for example, and a reflected light is received by a light receiving device to determine a state of a rainfall based on a degree of a reduction in a quantity of receipt of a light or a manner of a temporal change.
As shown in FIG. 6, a change in a light receiving quantity signal sent from the light receiving device in the case in which general raindrops adhere to the raindrop detecting surface is once reduced rapidly for 2 msec, for example, and is then returned into an increasing direction and tends to be stabilized, and a decrease in a reflectance is comparatively small, and therefore, a change in a quantity of receipt of a light is not great, that is, approximately 3%.
This depends on the fact that a raindrop colliding with a windshield has a shape changed by a surface tension thereof as is also indicated in JP-A-2006-7936.
The raindrop detecting surface is set to have a small area in order to prevent a field of view from being disturbed. For this reason, conventionally, it is necessary to carry out a detection with a high sensitivity in order to perform a proper autowiper control. In a conventional autowiper controller, therefore, a decrease of 1.5% in a quantity of receipt of a light is set to be a threshold of the raindrop detection, for example.
At night or early in the morning in which a temperature is low, a phenomenon in which condensation occurs over a windshield appears. The phenomenon depends on the fact that a moisture in the air is solidified over an external surface of the cold windshield and thus becomes dewy as a minute waterdrop.
A speed of a change in a quantity of receipt of a light reflected from a raindrop detecting surface in the condensation process is lower than that in the case in which a raindrop adheres. However, a quantity of small waterdrops which adhere is increased to reach the whole raindrop detecting surface. For this reason, a decrease in a quantity of receipt of a light with a progress of condensation features to be increased more greatly as compared with the case in which the raindrop adheres.
The progress of the condensation is slow and the adhering waterdrops are not recognized by eyes of a driver to some extent. If a wiper repetitively carries out wiping over the windshield frequently with a small change in the quantity of receipt of a light, however, the driver feels troublesome.
In other words, there is a tendency that the driver generally wants to immediately wipe away the raindrop adhering to the windshield and desires to wipe away the condensation of the windshield at a great interval.